1. Field of the Invention
The present invention relates to the field of displaying technology, and in particular to a method for manufacturing a TFT (Thin-Film Transistor) substrate having storage capacitors and the TFT substrate.
2. The Related Arts
Flat panel displays have a variety of advantages, such as thin device body, low power consumption, and being free of radiation, and are thus widely used. Currently available flat panel displays generally include liquid crystal displays (LCDs) and organic light emitting displays (OLEDs)
Organic light emitting displays (OLEDs) have a variety of superior properties, such as being self-luminous, requiring no backlighting, high contrast, reduced thickness, wide view angle, fast response, applicability to flexible panels, wide range of operation temperature, and having simple structure and manufacturing process, and are regarded as emerging technology of the next generation of the flat panel displays.
In the manufacture of OLED panels, oxide semiconductors have been widely used due to having relatively high electron mobility and, compared to low-temperature poly-silicon, the oxide semiconductors having a simple manufacturing process and being of high compatibility to amorphous silicon manufacturing process, and also being compatible to high generation manufacturing lines.
OLED can be classified, according to the way of driving, into passive OLED (PM-OLED) and active OLED (AM-OLED).
A conventional AM-OLED device is generally made up of two transistors between which a storage capacitor is formed, of which an equivalent circuit is shown in FIG. 1, wherein a storage capacitor Cst is formed between a the thin-film transistor T1 and a thin-film transistor T2. The thin-film transistors T1, T2 are both field effect transistors. The thin-film transistor T1 serves as a signal switching transistor, which functions for supplying and cutting off a data signal. The thin-film transistor T2 serves as a driving transistor, which is connected to an organic light-emitting diode D. The storage capacitor Cst is generally composed of a gate terminal metal, a source/drain terminal metal, and an insulation layer interposed therebetween or a source/drain terminal metal, a pixel electrode, and an insulation layer interposed therebetween. Specifically, the signal switching transistor T1 has a gate terminal that receives a scan signal Vgate and a source terminal that receives a data signal Vdata, and a drain terminal connected to a gate terminal of the driving transistor T2. The driving transistor T2 has a source terminal connected to a power supply Vdd, a drain terminal connected to an anode of the organic light-emitting diode D. A cathode of the organic light-emitting diode D is connected to ground Vss. The storage capacitor Cst is connected between the drain terminal of the signal switching transistor T1 and the source terminal of the driving transistor T2.
The principle of the operation of the circuit is that when the scan signal Vgate is supplied, the signal switching transistor T1 is conducted and the data signal Vdata is fed to the gate terminal of the driving transistor T2 and amplified by the driving transistor T2 to drive the organic light-emitting diode D for performing displaying. When the scan signal is ended, the storage capacitor Cst serves as a major measure to maintain the potential level of the pixel electrode and a unified and expanded storage capacitor can effectively improve homogeneity of the displayed image and enhance the displaying quality. A measure for expanding the storage capacitor Cst generally involves two ways of either expanding the surface area of electrode plates or reducing the distance between two electrode plates. However, expanding the surface area of Cst would result in reduction of the area of the aperture zone, leading to reduction of aperture ratio and reduction of displaying brightness; and simply reducing the distance between two electrode plates would pose a potential issue of breaking through, leading to a risk of damaging the AM-OLED.